It is desired in the security field to more accurately determine if an intruder has entered a protected space. A common method of accomplishing this is to use dual technology motion detectors consisting of a Doppler microwave frequency motion detector and a passive infrared (PIR) detector. The PIR detector senses infrared radiation (IR) from the intruder while the Doppler microwave frequency motion detector transmits a microwave frequency signal and detects a change in the return signal due to the presence of an intruder. However, the PIR has inherent weaknesses that prevent it from detecting an intruder when the intruder moves directly at the sensor, when the ambient temperature is high, or when the intruder is cloaked, while the microwave frequency motion detector's inherent weakness is that false alarms occur when the detected motion is from a person outside the protected space or from a vibration of an object within the protected space. The typical operation of a dual technology motion detector is that the detector will generate an alarm signal when the PIR detector and the microwave frequency motion detector both detect the intruder. The combination of the detectors eliminates false alarms due to the microwave frequency motion detector detecting motion from a person outside the protected space or from vibration of an object within the protected space, but does not eliminate the inherent weakness of the PIR detector. It is desirable to use a microwave frequency motion detector, which detects all motion from an intruder, without the PIR detector and without false alarms. One way to reduce the false alarms associated with a microwave motion detector without the PIR detector confirmation is to accurately determine the location and movement of the intruder inside and outside the protected space in addition to detecting the intruder's motion. This allows vibrations, which over time do not change location, to be discriminated against. Additionally, if the microwave frequency motion detector also knows the perimeter of the protected space, it can discriminate against detected motion that is outside the perimeter of the protected space.
Furthermore, since the microwave frequency motion detector has a wider field of view than a PIR, it can provide wider coverage to odd shaped rooms and can detect motion outside a wall. Being able to detect motion inside the protected space and outside the protected space allows the detector to generate a warning when an intruder is moving towards the protected space but has not yet intruded, or generate an alarm when the intruder has transitioned from outside the protected space to inside the protected space. Detecting a transition from outside the protected space to inside the protected space allows a user to remain in the protected space without generating false alarms and while continuing intrusion protection of the protected space by the motion detector. This “nighttime” mode (where user turns the alarm system on while present in the protected space) is typically accomplished by use of magnetic door sensors. It is desirable to use one microwave frequency motion detector for all modes.
It is therefore an object of the present invention to be able to provide a reliable microwave motion detector that does not need to operate in conjunction with PIR devices as in dual technology devices of the prior art.
It is also an object of the present invention to be able to provide a reliable microwave motion detector that can differentiate motion outside the protected space from motion within the protected space.